Computerized Tomography (CT) is generally performed using a dedicated CT system, which is an expensive piece of equipment, found in limited numbers within the health care environment, and generally, because of its size and weight, in dedicated locations within the health care facility. It is very rare to find a CT system located in the operating room, where it would be available for intraoperative imaging. On the other hand, the C-arm type of X-ray fluoroscopic imaging system is a reasonably low cost piece of equipment, very widely found in both hospitals and clinics, and generally sufficiently mobile that it can be moved to the patient at the point of care or in the operating room. A number of prior art publications have described systems for providing three dimensional, CT-type, imaging information, using the two-dimensional imaging data provided by common C-arm systems. Such systems should be able to provide CT-type information using a system only a fraction of the cost of a dedicated CT system. At least one such a system is also available commercially, and it appears to use a motor to slowly rotate the C-arm in a controlled manner, stopping at predetermined incremental positions of the C-arm motion to generate fluoroscopic images.
One such C-arm based CT system is described in European Patent Application for “X-Ray photographing apparatus and method capable of performing computerized tomography using C-arm”, published as EP 0917855. This application, while describing some conceptual elements of the aims and advantages of such a system, does not appear to contain essential enabling details. Other such systems are described in U.S. Pat. No. 6,049,582 to N. Navab for “C-arm Calibration Method for 3-D Reconstruction”, U.S. Pat. No. 7,142,633 to J. W. Eberhard et al., for “Enhanced X-ray Imaging System and Method”, and in US 2006/0182216 to G. Lauritsch et al., for “Method for Reconstructing a CT Image using an Algorithm for a Short-Scan Circle combined with Various Lines”. In addition, U.S. Pat. No. 6,038,282, to K. Wiesent et al., describes a method and apparatus for generating in an X-ray C-arm imaging system, a voxel-driven back projection without the calculation of positional coordinates and physical focus and detection positions. U.S. Pat. No. 5,706,324, also to K. Wiesent et al., describes a method and apparatus for the use in a CT system of special marks which are imaged during scanning, and by which the geometry of the image can be determined.
In U.S. Pat. No. 6,666,579 for “Method and Apparatus for Obtaining and Displaying Computed Tomography Images using a Fluoroscopy Imaging System”, to V. T. Jensen, there is described a C-arm system which provides CT-type information for diagnostic purposes and interventional procedures. The system includes a C-arm having an x-ray source and a receptor for obtaining fluoroscopic images of a patient. The C-arm is moved through an image acquisition path along which at least first and second images are obtained. An acquisition module obtains multiple 2-D fluoroscopic images at desired positions along the image acquisition path and an image processor constructs a 3-D volume of object data based on the 2-D fluoroscopic images. Patient information is displayed based upon the 3-D volume of patient information. A position tracking system is included to track the position of the receptor, patient and (if included) a surgical instrument. The position information is used to control the time at which exposures are obtained and (if included) to superimpose instrument graphical information on a display with patient information.
However, this system appears to be a dedicated system, including a number of additional accessory components not generally found in the common C-arm fluoroscope imager, in particular, the tracking system required to define the positions of the source, subject, detector and surgical tool if present. Although considerably less costly than a CT system, this system does involve the capital expenditure of the new equipment, or the cost of amending an existing C-arm fluoroscope by installation of the additional features required for its operation.
There therefore exists a need for a system for obtaining CT-type information from the outputs of conventional existing, C-arm fluoroscopic imaging systems, by means of simple software routines, without the need to make any changes or additions to the structure of the existing C-arm fluoroscope, thus overcoming at least some of the disadvantages of prior art systems and methods.
The disclosures of each of the publications mentioned in this section and in other sections of the specification are hereby incorporated by reference, each in its entirety.